The categories seem balanced out to me. There's 1 for gameplay, 1 for visuals, 1 for audio and 1 for how well it worked with the 64x64 rule. While the visuals and authenticity categories are the ones closest to each other, I still feel they're different enough that they deserve separate categories.
A simple 64x64 game with a 1 pixel player character and nothing else would not be visually pleasing, but it would get the highest authenticity score from me, simply because it's a proper 64x64 game. The opposite might be a great looking game where the UI is in a higher resolution than 64x64. So while it's true that visuals and authenticity are both visual categories, they are about very different things.
Merging audio and visuals into 1 category doesn't seem like a good idea to me, even though it would probably benefit me, as I barely have audio haha :P. What kind of gameplay-centric categories do you have in mind?
I think it's also a matter of what you find important. For me, I try to score highest with authenticity and gameplay. I don't care much for my score on visuals and audio. And maybe that's the reason why the categories feel balanced out to me. :P